Study On The Modification Of Corn Stalk Pyrolysis Carbon And Its Adsorption Performance Of Heavy Metal Ions And Phenol

In recent years,problems such as greenhouse effect,environmental pollution and energy shortage caused by fossil fuel combustion have become increasingly prominent.High-value conversion and utilization of biomass is considered as a key substitute to solve environmental and energy problems.The thermochemical conversion of biomass is one of the important ways to realize the utilization of biomass.Solid biochar produced by pyrolysis is environmentally friendly and inexpensive.After doping and activation,biochar generally contains abundant pore structures,high surface area,abundant surface oxygen-containing functional groups and other characteristics,and has good biological affinity and adsorption performance.At the same time,the annual output of lignocellulosic straw biomass raw materials is huge in China.The rational utilization of straw resources can not only improve the added value of agricultural and forestry residues,increase farmers’income,but also solve the environmental pollution caused by the straw burning.Lead and chromium are common metal elements in production and life,and widely used in machinery industries,iron and steel smelting and other industries.Phenol is an important organic raw material,which is widely used in the manufacture of phenolic resin and herbicide.However,during the production and application of lead,chromium and phenol substances,a large number of solid waste or wastewater containing lead,chromium and phenol are abandoned to the natural environment,which will not only cause environmental pollution,but also affect human health.The conversion of biomass into functional materials with high adsorption performance for the adsorption of pollutants such as lead,chromium and phenol in wastewater is of great significance for promoting the utilization of biomass with high value and strengthening environmental protection.Therefore,in this work,using corn straw as raw material,a one-step pyrolysis activation method was used to obtain mesoporous biomass carbon materials with high nitrogen content for adsorption of lead,chromium and phenol.The adsorption properties of nitrogen-doped modified carbon on Pb（Ⅱ）and Cr（Ⅵ）heavy metal ions and phenol organic compounds in aqueous solution were studied in depth,and the adsorption mechanism was discussed respectively.The research content of this thesis is mainly divided into the following two parts:（1）Corn stalk based nitrogen-doped mesoporous carbon was prepared by one-step carbonization and activation.The effect of changing the activation temperature and modifying agent ratio modification conditions on the pore structure and surface functional groups of the pyrolytic carbon was compared,and the obtained nitrogen-doped mesoporous carbon was used to remove Pb（Ⅱ）and Cr（Ⅵ）heavy metal ions from water.The effects of pyrolysis temperature,nitrogen ratio and p H on the adsorption effect were systematically studied.The results showed that the maximum adsorption capacity of KHC700-1 on Pb（Ⅱ）was 222.86 mg/g,and that of KHC700-0.25 on Cr（Ⅵ）was 259.00mg/g.Adsorption kinetics and isotherm analysis showed that the adsorption of Pb（Ⅱ）and Cr（Ⅵ）by the modified carbon is mainly chemical adsorption.The mechanism analysis shows that the possible mechanisms for the adsorption of Pb²⁺ions by the corn stalk based nitrogen-doped mesoporous carbon include pore filling mechanism,electrostatic interaction,ion exchange and complexation,and the possible mechanisms for the adsorption of HCr O₄^-and Cr₂O₇^2-ions include pore filling,electrostatic interaction and ion exchange mechanism.（2）The as-prepared corn stalk based nitrogen-doped mesoporous carbon was used to remove phenol,a typical organic pollutant in water,and the influence of pyrolysis temperature,nitrogen ratio and p H on the adsorption effect was also systematically studied.The corn stalk based nitrogen-doped mesoporous carbon showed good adsorption effect on phenol,and the adsorption capacity of KHC700-0.5 was 246.00 mg/g at p H=5.The analysis of adsorption isotherms and adsorption kinetics showed that the adsorption of phenol on KHC700-0.5 mainly consisted of intramolecular monolayer adsorption and chemisorption.The mechanism analysis showed that the adsorption mechanisms for the adsorption of phenol,include pore filling,electrostatic attraction,π-πinteraction and Lewis acid-base interaction.The competitive adsorption results of phenol with Pb（Ⅱ）,Cr（Ⅵ）,Cu（II）and nitrate showed that both anions and cations had competitive adsorption effects on the adsorption of corn stalk based nitrogen-doped mesoporous carbon for phenol,resulting in the reduction of adsorption capacity.The research results of this thesis can provide valuable reference for efficient adsorption of heavy metal ions and phenol organic pollutants from water by corn stalk derived pyrolytic carbon.